1. Field of the Invention
The invention relates to a novel process for preparing styryl dyes and to the use of thus prepared styryl dyes for mass coloration of organic polymeric materials and for dyeing polyester fibres from aqueous media.
2. Brief Description of the Prior Art
CH-A-56 9055 describes styryl dyes for dyeing polyester fibres and for mass coloration of specific plastics. The preparation of these dyes by the process of CH-A-56 9055 is costly and inconvenient. This is because the dyes have to be purified by recrystallization before they can be industrially used at all.
Especially in relation to the compounds of Examples 9 and 10 of CH-A-56 9055, it has been determined that the as-prepared compounds change in the course of storage to become dull and unattractive without purification or recrystallization.
In fact, the unrecrystallized dyes turn reddish and dull in the course of 24 months just on standing at 25° C. At temperatures of >50° C. such as are possible in tropical regions or which prevail in some warehouses, the dyes change significantly faster. The decomposition of the unrecrystallized dyes is also further enhanced by the presence of polyglycols, the addition of which is advantageous for use in granular form.
It is an object of the invention to provide a process for preparing styryl dyes that are free of the prior art disadvantages and, more particularly, provide styryl dyes which are more stable in storage.